In the construction industry or in the building of new infrastructure or re-building of existing infrastructure, it is customary to lay cable and cable bundles which extend long distances in conduit pipe. Conduit pipe is essentially a pipe provided to serve as a channel or container in which the electrical cable is permanently housed. Typically, the conduit pipe is embedded in the ground or in a wall, and the cable or cable bundle is pulled through the conduit by hand or by mechanical means, such as with a winch. In general, the conduit pipe is provided with a diameter considerably larger than the diameter of the individual cables or cable bundle being housed by the conduit. However, large friction forces develop between the cable and the interior conduit walls, making it difficult to pull the cable through the conduit. If lubrication is used, it is customary to lubricate the cable or cable bundle at the entry end of the conduit to minimize the friction between the cable and the conduit walls. A lubricant is applied from the container directly to the cable or cable bundle as the cable is pulled through the conduit. A petroleum-based lubricant may be applied by hand onto the surface of the cable. U.S. Pat. No. 3,925,216 discloses a lubricant in the form of a liquid comprising an alcohol water solution of polyethylene oxide. U.S. Pat. No. 4,111,820 discloses a coating composition consisting essentially of an aqueous solution of a dispersion agent and polyethylene oxide. U.S. Pat. No. 4,378,299 discloses a lubricant in liquid or gel comprising an aqueous solution of from about 1 to 4% of a water soluble cellulose derivative containing about ½ to 2 wt. % of polyacrylamide. U.S. Pat. No. 5,002,675 discloses another cable lubricating composition including 10-30 wt. % propylene glycol, 0.1-1 wt. % sodium carboxymethyl cellulose, 0.01-1 wt. % hydroxyethyl cellulose, and 0.01-1 wt. % methyl paraben.
In practice, the petroleum-based lubricants of the prior art are often wiped or scraped from the cable soon after the particular section of cable has been drawn into the conduit. This makes further pulling difficult. The known aqueous-based pulling compositions can be stiff and nonthixotropic, can be hard to handle and apply to the surface, and can fail to reduce the coefficient of friction under a broad load range. The prior coatings can also be electrically conductive while they are wet, which makes them dangerous to use in a live circuit and/or extends the time before the power to the circuit can be turned on.
The invention relates to a novel composition for coating/lubricating cable strands, imparting them with excellent coefficient of friction properties; a novel apparatus for lubricating cable strands; and a method to lubricate and pull cable strands through a conduit. In one embodiment of the invention, the lubricating composition is in the form of a powder form, which adheres to the cable surface and facilitates pulling the cable strands through a conduit.